Hydraulic trim tilt systems for outboard propulsion units are well-known. Further, such systems' units employing a single cylinder to displace the propulsion system such as rotating them through an arc are well-known. One such example is shown in U.S. Pat. No. 3,799,104.
U.S. Pat. No. 3,842,789 also shows a system for using a single cylinder for power trim and tilt. U.S. Pat. Nos. 4,064,824 and 4,096,820 both show systems for applying hydraulic forces to separate trim and tilt cylinders. Other patents showing hydraulic systems used with marine propulsion units are U.S. Pat. Nos. 3,885,517; 3,434,450 and 3,434,448.
All of the prior systems, U.S. Pat. No. 3,842,789 being an example, require a particular valving arrangement to change the amount of hydraulic pressure to the actuator and to rotate the propulsion unit through the trim and tilt range. In that patent, manual adjustment of a valve in the hydraulic supply lines is required. Although the object of this patent and of other patents is to provide a higher pressure to a system when requiring greater force and less rapid movement during trim operation and a lower pressure and more rapid movement during tilt operation, the prior devices either require separate actuator cylinders to rotate the propulsion unit through trim and tilt, or require special hydraulic switching systems to change the distribution area or the hydraulic fluid in the actuator.